In the past, it has been known that crude tall oil, consisting of approximately 35-50% fatty acids, including oleic, linoleic and palmitic acids, 15-55% rosin acids, and 5-35% unsaponifiable and neutral material, could be separated into its component parts by the use of vacuum and steam assisted fractional distillation procedures based on volatility. See, for example, U.S. Pat. Nos. 2,886,492 and 3,216,909. Such fractional distillation systems commonly use a first column to separate the more volatile fatty acids and rosin acids (referred to herein as the "volatile fraction") from the less volatile materials which include many of the unsaponifiable and neutral materials such as sterols and their esters (referred to herein as the "residue fraction" or "pitch"). A second column is commonly designed to separate the more volatile fatty acids from the less volatile rosin acids. For further discussion of such fractional distillation procedures of crude tall oil, see McSweeney, "Sulfate Naval Stores," in Naval Stores: Production. Chemistry. Utilization (D. F. Zinkel and J. Russell, eds., Pulp Chemicals Association, New York, 1989) at pp. 160-199.
In particular, such procedures in a first cut seek to separate at least about 95% of the fatty acids and at least about 90% of the rosin acids from the remaining components of the tall oil. This separation is typically accomplished by applying sufficient heat to the crude tall oil and to the residue fraction of the aforementioned first distillation column, such as by heating the residue fraction to at least about 300.degree. C., which causes the residue fraction to be substantially free of the more volatile components of tall oil, such as the fatty acids (less than about 5%) and the rosin acids (less than about 10%). Essentially all of the high boiling neutral components of the tall oil remain with the pitch, which includes esterified sterols. Non-esterified alcohols, however, are more likely to boil off. Additionally, non-esterified sterols are easily degraded by the high temperature. For example, more than half of the .beta.-sitosterol found in crude tall oil is destroyed by the high temperature used to optimize for separation of the fatty and rosin acids from the other components.
There is a need for sources of sterols such as those included in tall oil. For example, .beta.-sitosterol has been indicated as an agent that promotes the reduction of circulating cholesterol in humans, and thus is a desirable additive for foods. A method of separating sterols generally, and .beta.-sitosterol in particular, wherein the sterols are not or substantially are not destroyed in the process, would be a useful invention in the chemical preparation industry.